Synthesis of bimetallic oxide nanocomposites using poly (ionic liquid)

ABSTRACT

A method of synthesizing bimetallic oxide nanocomposites includes the steps of: providing a first metal salt solution; adding an oxidizing agent to the first metal salt solution while degassing the solution with an inert gas; heating the first metal salt solution; adding a second metal salt solution to the heated first metal salt solution to form a reaction mixture; adding a solution comprising a poly (ionic liquid) into the reaction mixture; adding a first base into the reaction mixture; adding a second base while stirring and maintaining a temperature ranging from about 40° C. to about 65° C. to provide a solution including a bimetallic oxide nanocomposite precipitate. The first metallic salt solution can include FeCl 3  dissolved in water. The second metallic salt solution can include CuCl 2  dissolved in water. The bimetallic oxide nanocomposites can be combined with epoxy resin to coat a steel stubstrate.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to bio-nanotechnology and, particularly,to the synthesis of Cu₂O.2Fe₃O₄ nanocomposites capped with poly(ionicliquid) for use as highly dispersed fillers.

2. Description of the Related Art

Epoxy resins are commonly used as organic coatings to protect steel fromcorrosion. Epoxy resins are excellent corrosion inhibitors anddemonstrate good adhesion for steel substrates. Drawbacks ofconventional epoxy coatings, however, include the appearance ofmicrocracks, holes, low thermal and fire retardant stability, andtoughness.

Thus, a method of synthesizing nanocomposites utilizing poly (ionicliquid) solving the aforementioned problems is desired.

SUMMARY OF THE INVENTION

A method of synthesizing bimetallic oxide nanocomposites includes thesteps of: providing a first metal salt solution; adding an oxidizingagent to the first metal salt solution while degassing the solution withan inert gas; heating the first metal salt solution; adding a secondmetal salt solution to the heated first metal salt solution to form areaction mixture; adding a solution comprising a poly (ionic liquid)into the reaction mixture; adding a first base into the reactionmixture; adding a second base while stirring and maintaining atemperature ranging from about 40° C. to about 65° C. to provide asolution including a bimetallic oxide nanocomposite precipitate. Thefirst metallic salt solution can include FeCl₃ dissolved in water. Thesecond metallic salt solution can include CuCl₂ dissolved in water. Theoxidizing agent can be sodium sulfite (Na₂SO₃). The bimetallic oxidenanocomposite can be Cu₂O.2Fe₃O₄. The bimetallic oxide nanocompositescan be combined with epoxy resin to coat a steel stubstrate.

These and other features of the present invention will become readilyapparent upon further review of the following specification anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing the synthesis of polyionic liquid based onAMPSA-VP.

FIG. 2 is a schematic showing the synthesis of Cu₂O.Fe₃O4 in thepresence of AMPSA-VP2.

FIG. 3 shows the ¹HNMR spectra of (a) AMPSA/AAm, (b) AMPSA/MAA and (c)AMPSA/MAA.

FIG. 4 shows the ¹³C NMR spectra of a) AMPSA/AAm, b) AMPSA/MAA and c)AMPSA/MAA.

FIG. 5A shows the FTIR spectra of Cu₂O.2Fe₃O₄ (Example 2)

FIG. 5B shows the FTIR spectra of Cu₂O.2Fe₃O₄ (Example 3)

FIG. 6 shows the UV-visible spectra of Cu₂O.2Fe₃O₄ nanocomposites.

FIG. 7 shows the TGA thermograms of Cu₂O.2Fe₃O₄ nanocomposites.

FIG. 8A shows the XRD diffractogram of Cu₂O.2Fe₃O₄ (Example 2)

FIG. 8B shows the XRD diffractogram of Cu₂O.2Fe₃O₄ (Example 3).

FIG. 9A shows the SEM micrograph of Cu₂O.2Fe₃O₄ (Example 2).

FIG. 9B shows the SEM micrograph of Cu₂O.2Fe₃O₄ (Example 3).

FIG. 10A shows the TEM micrograph of Cu₂O.2Fe₃O₄ (Example 2).

FIG. 10B shows the TEM micrograph of Cu₂O.2Fe₃O₄ (Example 3).

FIGS. 11A and 11C show the HRTEM micrographs of Cu₂O.2Fe₃O₄ (Example 2).

FIGS. 11B and 11D show the HRTEM micrographs of Cu₂O.2Fe₃O₄ (Example 3).

FIG. 12A shows the DLS measurements of Cu₂O.2Fe₃O₄ (Example 3) inaqueous solution using 0.001 M KCl at 25° C.

FIG. 12 B shows DLS measurements of Cu₂O.2Fe₃O₄ (Example 2) in aqueoussolution using 0.001 M KCl at 25° C.

FIG. 13A is a graph showing Zeta potential measurements of Cu₂O.2Fe₃O₄(Example 3) in aqueous solution at 25° C.

FIG. 13B is a graph showing Zeta potential measurements of Cu₂O.2Fe₃O₄(Example 2) in aqueous solution at 25° C.

FIG. 14 is a graph showing the heat release rate curve of epoxy and itsblend with 5 wt. % of Cu2O.2Fe₃O₄ nanocomposites prepared using Example3.

FIG. 15 shows the smoke production rate curve of epoxy and its blendwith 5 wt. % of Cu₂O.2Fe₃O₄ nanocomposites prepared using Example 3.

Similar reference characters denote corresponding features consistentlythroughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method of synthesizing bimetallic oxide nanocomposites includes thesteps of: providing a first metal salt solution; adding an oxidizingagent to the first metal salt solution while degassing the solution withan inert gas; heating the first metal salt solution to a temperatureranging from about 40° C. to about 65° C.; adding a second metal saltsolution to the heated first metal salt solution to form a reactionmixture; adding a solution comprising a poly (ionic liquid) into thereaction mixture; adding a first base dropwise into the reaction mixturefor about 1 hour; adding a second base while stirring and maintaining atemperature between 40° C. to 65° C. for at least 2 hours to provide asolution including a bimetallic oxide nanocomposite precipitate. Thefirst metallic salt solution can include FeCl₃ dissolved in water. Thesecond metallic salt solution can include CuCl₂ dissolved in water. Theoxidizing agent can be sodium sulfite (Na₂SO₃). The bimetallic oxidenanocomposite can be Cu₂O.2Fe₃O₄. The first base can be sodium hydroxideand the second base can be ammonium hydroxide. The bimetallic oxidenanocomposites can be combined with epoxy resin to coat a steelstubstrate.

The poly (ionic liquid) can include poly(2-acrylamido-2-methyl-1-propanesulfonic acid-diethyl ethanolamine(PAMPS-DEA), 2-acrylamido-2-methyl-1-propanesulfonic acid-N-isopropylacrylamide (AMPS-NIPAm), 2-acrylamido-2-methyl-1-propanesulfonicacid-vinyl pyrrolidone (AMPS-VP), or2-acrylamido-2-methyl-1-propanesulfonic acid-acrylic acid (AMPS-AA).

The poly (ionic liquid) can be prepared by combining an ionic liquidmonomer and a co-monomer to obtain a mixture; adding a free radicalinitiator to the mixture and heating the mixture up to a temperature ofabout 70° C.; cooling the reaction mixture to obtain a polymeric ionicliquid product; dissolving the polymeric ionic liquid product in a firstorganic solvent to form a solution and precipitating out a solid or anoily polymeric ionic liquid product by adding the solution to a secondorganic solvent; and isolating the solid or the oily polymeric ionicliquid product by filtration. The synthesis process can be conducted inan inert atmosphere, for example, in nitrogen or argon. The firstsolvent and the second solvent can each include at least one of acetone,ethanol, and diethyl ether. The ionic liquid monomer can be2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) or a salt thereof.The co-monomer can include at least one of diethyl ethanolamine (DEEA),N-vinyl pyrrolidone (VP), acrylic acid (AA), and N-isopropyl acrylamide(NIPAm). The free radical initiator can be 2, 2-azobisisobutyronitrile,or any other suitable initiator.

The method of synthesizing bimetallic oxide nanocomposites can furtherinclude the steps of separating the precipitate by centrifuging at 15000rpm for about 10 minutes to isolate the bimetallic oxide nanocomposites;and washing the bimetallic oxide nanocomposites with distilled water.

The bimetallic oxide nanocomposites can have a mean diameter in therange of from about 1 nm to about 350 and a surface that is capped witha poly (ionic liquid). The bimetallic oxide nanocomposites can includeparticles of 10 nm-30 nm size belonging to the Fe₃O₄ nanospheres andparticles of 35 nm-300 nm belonging to rhombic dodecahedral Cu₂O.

The method of using a bimetallic oxide nanocomposite to coat a substrateincludes the steps of combining the bimetallic oxide nanocomposites witha prepolymer and a hardener under ultrasonic conditions for about 30minutes to form a homogenous mixture; spraying the mixture onto a cleansubstrate surface to provide a uniform layer; and curing the uniformlayer for about 1 week at a temperature of about 40° C. to coat thebimetallic oxide nanocomposite on the substrate. The substrate can be asteel plate. The prepolymer can be epoxy resin and the hardener can be apolyamide or polyamine polymer. A weight ratio of the bimetallic oxidenanocomposite can be from about 0.1 percent by weight to about 0.5percent by weight of the hardener and the polymer

In some embodiments, the nanoparticles disclosed herein are from about 1nm to about 250 nm in diameter, preferably about 1-50 nm.“Nanocomposites” are materials that incorporate nanosized particles thatare less than 100 nm in size into a matrix of standard material, such asa polymer matrix. “Poly (ionic liquids),” PILs, are a macromoleculararchitecture of functional materials based on ionic liquid (IL) monomersconnected through a polymeric backbone. The modification of PILcharacteristics (density, viscosity, and surface tension) are of greatimportance for their application.

The present methods provide Cu₂O.2Fe₃O₄ nanocomposites or Cu₂O doped oniron oxide nanoparticles (Fe₃O₄) capped by modified poly(ionic liquid)in one step to control their dispersion in aqueous and epoxy coatings,to produce new highly dispersed fillers having multi-purposes, and toimprove epoxy coatings performances of varied materials for diverseapplication requirements. The presence of copper-based frame sheets canimprove the interfacial fracture toughness of epoxy. Moreover, thedoping of Cu₂O with Fe₃O₄ can improve the fire retardancy of epoxyresins and increase adhesion of epoxy with steel substrate.

The present technology, thus generally described, will be understoodmore readily by reference to the following examples, which is providedby way of illustration and is not intended to limit the scope of thepresent technology.

The following materials were used as received.2-Acrylamido-2-methyl-1-propanesulfonic acid (AMPS), N-isopropylacrylamide (NIPAm), acrylonitrile (AN), N-vinyl pyrrolidone (VP),acrylic acid (AA) and acrylamide (AM), hydroxyl amine monomers wereobtained from Sigma-Aldrich Chemical Co. and used as received. Ammoniumpersulfate (APS) and 2,2-azobisisobutyronitrile (AIBN) were used ascrosslinker and radical initiators, respectively. Anhydrous ferricchloride, sodium sulfite, cupric chloride (CuCl₂.2H₂O) and sodiumhydroxide were used to prepare Cu₂O.2Fe₃O₄ composites. Diethylethanolamine (DEEA) was purchased from Sigma Aldrich Chemicals Co.

Example 1 Synthesis of Poly(Ionic Liquid) (PIL)

Equal molar ratios of AMPS and DEEA were mixed into a nitrogen purged 50ml flask at room temperature to dissolve AMPS for 8 hr to producetransparent light amber oil. AIBN (0.6 wt. % related to AMPS monomer)was added to the reaction mixture and the reaction temperature wasincreased up to 70° C. for 18 hr. The reaction mixture cooled to roomtemperature to produce transparent dark amber mixture. The product wasdissolved in ethanol with concentration of 20 Wt. % and precipitatedinto 5 folds of acetone and filtrated under vacuum. The wax whiteproduct was dried under vacuum to obtain transparent amber oil with %yield polymer 98.2% and melting temperature 42° C. The produced polymerwas designated as PAMPS-DEA.

A mixture of equal molar ratios (1:1 mol %) of AMPS and VP, NIPAm or AA(6 mmol of each monomer) was stirred with 6 mmol of DEEA under nitrogenatmosphere at 10° C. in flask. The mixing was carried out for 5 hrs tocomplete dissolution of AMPS in VP and DEEA solutions. Transparentsolution was obtained with yield of 99%, indicating the formation ofquaternized DEEA organic salt with VP and AMPS monomers. ABIN initiator(0.08 mmol) was added to the reaction mixture under nitrogen bubblingand the mixture was heated to 70° C. for 24 hrs. The viscosity ofmixture was increased and transparent light yellow mixture wasprecipitated from acetone into cold diethyl ether (dry ice/acetone bath)and collected after filtration. The viscous oil was dried under vacuumat 40° C. to remove any residual volatile materials to obtain AMPSA/VP,AMPSA/NPAm or AMPSA/AA polymer with high yield (98.7%).

Example 2 Synthesis of Cu₂O.2Fe₃O₄ Nanocomposites

FeCl₃ (13.4 g-23 g) was dissolved with 100 mL distilled water, andcharged into a 500 mL three-necked flask. The solution of 5-75 mL ofNa₂SO₃ (4.8 wt. %-14.5 wt. %) was added to the reaction mixture followedby bubbling with N₂ and stirring for 1 h. The reaction mixture washeated at temperature ranged from 40° C. to 65° C. The CuCl₂.2H₂O(1.75-7.4 g) was dissolved in 50 mL water was added to the reactionmixture, The solution of (1-2 M) of NaOH 100 mL in water was addeddropwise to the reaction mixture during 1 h. The ammonium hydroxide (4-8g) dissolved in 50 mL aqueous solution was added to the reaction mixturewas added at the same time with solution of (1-2 M) of NaOH 100 mL inwater and at temperatures ranging from about 40° C. to about 65° C. for2-10 h. The suspended brownish black solution was centrifuged at 15000rpm for 10 min. The precipitate obtained was washed several times withdistilled water to remove the NaCl and other salts from the solvent. TheCu₂O.2Fe₃O₄ nanoparticles were dispersed in distilled water, andadjusted (pH 2) with 2 mol/L HCl for further experiment. The yieldpercentage of the reaction ranged from 85% to 95%.

Example 3 Synthesis of Cu₂O.2Fe₃O₄ Nanocomposites

FeCl₃ (13.4-23 g) was dissolved with 100 mL distilled water, and chargedinto a 500 mL three-necked flask. The solution of 5-75 mL of Na₂SO₃(4.8-14.5 wt. %) was added to the reaction mixture followed by bubblingwith N₂ and stirring for 1 h. The reaction mixture was heated attemperature ranged from 40 to 65° C. The CuCl₂.2H₂O (1.75-7.4 g) wasdissolved in 50 mL water was added to the reaction mixture. ThePAMPS-DEA, AMPSA/VP, AMPSA/NPAm or AMPSA/AA polymer (2-8 g) wasdissolved in 50 ml and added to the reaction mixture. The solution of(1-2 M) of NaOH 100 mL in water was added dropwise to the reactionmixture during 1 h. The ammonium hydroxide (4-8 g) dissolved in 50 mLaqueous solution was added to the reaction mixture at the same time withsolution of (1-2 M) of NaOH 100 mL in water at temperatures ranging fromabout 40° C. to 65° C. for 2-10 h. The suspended brownish black solutionwas centrifuged at 15000 rpm for 10 min. The precipitate obtained waswashed several times with distilled water to remove the NaCl, and othersalts from the solvent. The Cu₂O.2Fe₃O₄ nanoparticles were dispersed indistilled water, and adjusted (pH 2) with 2 mol/L HCl for furtherexperiment. The yield percentage of the reaction ranged from 96 to 99%.

The chemical structure of the PAMPS-DEA was confirmed by ¹H- and ¹³CNMRanalyses that were recorded on a 400 MHz Bruker Avance DRX-400spectrometer. The surface morphology of the nanogels was observed by(SEM) (JEOL DCA-840A) instrument at 20 kV. A few droplets of the dilutedsuspension were dropped on to a cover glass and then dried under vacuumat room temperature for 24 hours. Samples were coated with gold vaporprior to observation. The morphology of nanogels was observed underTransmission Electron Microscope (TEM, JEOL JEM-2100 F) electronmicroscope. High resolution HR-TEM images recorded an accelerationvoltage of 200 kv. The TEM sample was prepared by placing a dilute dropof aqueous particles onto the copper grids and allowing it to dry.

The analysis was performed using a Bruker D2 Phaser X-ray powderdiffractometer (30 kV, 10 mA) using Cu anode (k=0.15406 nm) at 250 C.The patterns were collected in the 2 [theta] range of 4-700 with stepsize of 0.020 and scan rate of 1 s.

Zeta potentials were determined using Laser Zeta meter MalvernInstruments (Model Zetasizer 2000) in aqueous solution in the presenceof KCl (0.01 M) at different pH solutions.

The thermal stability and nanogel contents of nanogel composites wereevaluated using thermogravimetric analysis (TGA; TGA-50 SHIMADZU at flowrate 50 ml/min and heating rate of 20° C./min).

The dispersion stability, polydispersity index (PDI) and surface charges(zeta potential; mV) of nanogel composites were determined by usingdynamic light scattering (DLS; Laser Zeta meter Malvern Instruments;Model Zetasizer 2000). UV-Vis spectrophotometer (UV-2450, Shimadzu,Kyoto, Japan) was used to confirm the formation of nanocomposites atwave lengths ranged from 200 to 700 nm.

Example 4 Preparation of Cu₂O.2Fe₃O₄ Epoxy Nanocomposite Coatings

Cu₂O.2Fe₃O₄ nanocomposites prepared using the methods described inExample 2 or 3 were blended with epoxy resins at weight percentagesranging from 0.1 to 5 wt. % based on total weight of epoxy and hardenerunder sonication for 30 minutes. The dispersed Cu₂O.2Fe₃O₄ epoxycomposites were mixed with polyamide hardener under vigorous stirringaccording to the recommended volume ratios resin/hardener (4/1). Themixtures were sprayed on blasted and cleaned steel panels to obtain dryfilm thickness (DFT) of 100 μm and cured for 1 week at temperature 40°C. to be sure the all epoxy films were cured.

Tests of the coated epoxy nanocomposite films were performed as follows.The blasting of steel panels, mechanical tests such as T-bending, impactresistance, hardness and pull-off adhesion test were carried outaccording standard methods ASTM. The adhesion pull-off test wasdetermined using a hydraulic pull-off adhesion tester in the range of0-25 MPa. The hardness was determined by using Erichsen hardness testpencil, model 318S, scratching force in the range of 0.5-20 N. Theabrasion resistance was evaluated according ASTM D4060-07 by applying5000 cycles with 1000 g load on the tested panels. A salt spray cabinet(manufactured by CW Specialist equipment ltd. model SF/450) was used toevaluate the salt spray resistance of coated panels. The tests werecarried out for cured epoxy nanocomposite films in the presence orabsence of Cu₂O.2Fe₃O₄ nanocomposites on steel panels. ASTM B117 wasused to investigate salt spray tests.

The flammability of the sample was measured by an FTT cone calorimeterinstrument (U.K.) under heat flux of 35 kW/m2 according to ISO 5660-1.The size of specimen was 100×10³ mm³.

The quaternization of DEA with AMPS polymers succeeded to prepare newPILs. PAMPSA was prepared and showed excellent thermal stability andsurface active properties for use as super filler for epoxy coatingswith multi-functional purposes, e.g., to protect carbon steel. In thepresent invention, AMPS is selected to prepare copolymers with VPmonomer that has great efficacy to act as stabilizing, capping andreducing agent when converted to poly(vinyl pyrrolidone), PVP, at thesame time to prepare controlled shapes and sizes of nanomaterials.Moreover, the reactivity ratios data between AMPS and VP confirmed thatthe alternate copolymers were prepared during the copolymerization ofAMPS and VP. The scheme of copolymerization of quaternized EDA withAMPS/VP copolymers is represented in FIG. 1. It is expected that theAMPSA/VP can be used as capping for formation of Cu₂O.2Fe₃O₄nanoparticles at room temperature to increase their wetting andadsorption characteristics at different interfaces.

The mechanism for preparing the Cu2O.Fe₃O₄ in the presence of NaOH andNH₂OH can be represented in the following equations:6Fe³⁺+SO₃ ²⁻+O²⁻

SO₄ ²⁻+2Fe²⁺+4Fe³⁺  (1)2Fe²⁺+4Fe³⁺+18OH⁻

2Fe₃O₄+9H₂O  (2)2Cu²⁺+NH₂OH

2Cu⁺+(NHOH)+2H⁺  (3)(NHOH)+½O₂

NO₂ ⁻+H⁺  (4)2Cu⁺+2OH⁻

Cu₂O+H₂O  (5)6FeCl₃+2CuCl₂+Na₂SO₃+23NaOH+NH₂OH+½O₂

Cu₂O.2Fe₃O₄+Na₂SO₄+NaNO₂+22NaCl+13H₂O  (6)

These equations represent the oxidation reduction reactions to convertthe ferric chloride and cupric chloride salt to produce Cu₂O.2Fe₃O₄composites.

One of the most important goals of the present work is to use poly(ionic liquid) PIL as reducing and capping agents to produce silvernanoparticles with controlled shape and size. For this purpose, VP isused as co-monomer with AMPSA (FIG. 1) to produce PIL having greatertendency to reduce silver metal ions to metal nanoparticles. Moreoverthe presence of DEEA in the chemical structure of AMPSA/VP assists inreduction of silver ions to silver metal due to the presence of hydroxylgroup. In the present work, AMPSA/VP was used to produce Cu₂O.2Fe₃O₄ ina simple one-step method. It is postulated that the PIL surrounded thecuprous, ferric and ferrous cations into a flexible network by polarinteractions between cations and negative anions of AMPSA/VP chains toproduce stable hydrosol. It is expected that there are two possiblemechanisms to illustrate the reduction step: direct hydrogen abstractionof PIL of VP backbone induced by the cations and/or reducing action ofVP macroradical formations.

The chemical structures of the prepared PILs PAMPSA and PAMPSA/VP areconfirmed from ¹H and ¹³C NMR spectra as presented in FIGS. 3 and 4. Theprotons of PAMPSA were elucidated from previous works and confirmed onthe chemical structure of PAMPSA/VP (FIG. 3). The disappearance of HC═peaks at chemical shifts from 5.1 to 6.4 ppm elucidates thecopolymerization of AMPSA/VP copolymer. The appearance of a broad peakat 8.3 ppm elucidates the de-shield proton of quaternize amine groups ofDEA with AMPS sulfonate group (FIG. 3). The presence of new peaks at 3.1and 3.7 ppm (attributed to methylene groups of VP) confirms thecopolymerization of VP to form AMPSA/VP without degradation orhydrolysis by sulfonate group of AMPS.

The ¹³C NMR spectrum was also used to confirm the copolymerization ofAMPSA with VP as represented in FIG. 4. The disappearance of peaks atchemical shifts from 110 to 130 ppm, C═C, elucidates the polymerizationof PAMPSA and PAMPSA/VP. The presence of peaks at δ 168.58 (CON), 77.3(C—O of DEA), 60.06 (C—N⁺), 58.13 (C—SO₃ ⁻), 40.3 (C—SO₃ ⁻) 26.84 (CH)and 10 ppm (CH₃) elucidates the polymerization and quaternization ofPAMPSA and PAMPSA/VP.

The Cu₂O.2Fe₃O₄ nanocomposites were characterized as follows. Thechemical structures of the Cu₂O.2Fe₃O₄ composites prepared in absence ofPIL (Example 2) and in the presence of PIL (Example 3) were determinedby FTIR and are represented in FIGS. 5A and 5B, respectively. Thepresence of Fe₃O₄ and Cu₂O was elucidated by appearance of absorptionbands at 580 and 626 cm⁻¹ respectively, which are ascribed to Fe—O andCu—O bond vibration. The appearance of organic functional groups of PILat 3442, 1632 and 1037 cm⁻¹, attributed to OH, CONH and C—O stretchingof PIL, in the spectrum of Cu₂O.2Fe₃O₄ composites prepared in PIL(Example 3; FIG. 5B) confirms the encapsulation of composite into PIL asproposed in FIG. 2.

The formation of Cu₂O.2Fe₃O₄ nanoparticles with or without AMPSA/VP canbe elucidated from UV-visible spectrum represented in FIG. 6. TheCu₂O.2Fe₃O₄ nanocomposites have absorption in the whole UV-visibleregion ranging from 200 nm to 700 nm. The formation of plasmonelucidates that magnetite was not formed separately but was doped withCu₂O during a short time elucidates the ability of AMPSA/VP to act aseffective reducing and capping agent at temperature of 50° C.

The thermal stability of Cu₂O.2Fe₃O₄ nanocomposites and the content ofAMPSA/VP can be determined from the TGA thermograms represented in FIG.7. The data confirmed that there is approximately 3.8 wt. % of boundwater and hydroxyl groups formed at the Cu2O.2Fe3O4 surfaces which lostat temperature ranging from 25 to 150° C. The contents of AMPSA/VP aredetermined as 4 wt. % that lost at temperatures ranging from 350 to 420°C. The data also confirmed the high thermal stability of Cu₂O.2Fe₃O₄nanocomposites.

The crystal structure of Cu₂O.2Fe₃O₄ nanocomposites can be determinedfrom XRD patterns as represented in FIG. 8. Seven major reflectionslocated at about 30.1°, 35.5°, 43.2°, 53.5°, 57.1°, 62.6° and 74.3°shown in FIG. 8A can be assigned to diffraction of Fe₃O₄ nanoparticleswith cubic-phase from the (220), (311), (400), (422), (511), (440) and(533) planes (JCPDS card No. 65-3107), respectively. The peaks at 2θvalues of 36.5°, 42.4° and 61.4°, are clearly distinguishable and can beperfectly indexed rhombic dodecahedral crystals in the cubic-phase fromthe (1 1 0), (1 1 1), (2 0 0), (2 1 1), (2 2 0), (3 1 1) and (2 2 2)planes (JCPDS card No. 05-0667). These peaks correspond to the crystalplanes of (111), (200) and (220) of the Cu₂O, respectively. These peakssuggest that Cu₂O.2Fe₃O₄ nanocomposites are formed. XRD pattern of theCu₂O.2Fe₃O₄ nanocomposites reveals that the crystal structure of Fe₃O₄is well-maintained after loading by Cu2O during the reaction process. Itwas clear that the intensity of the Cu2O peaks became gradually strongerwith the presence of AMPSA/VP during of the formation of Cu₂O.2Fe₃O₄nanocomposites (Example 3). On the other hand, it was notable that therewas a slight positive shift for the diffraction peaks (3 1 1), (2 0 0),(5 1 1), (2 2 0), (3 1 1) at approximately 35.5, 43.2, 57.1, 61.5, 77.6,indicating that there was an interaction between Cu₂O and Fe₃O₄. The lowintensity and broadness of peaks for Cu₂O.2Fe₃O₄ nanocomposites preparedin the presence of AMPSA/VP (FIG. 8B; Example 3) elucidate the lowparticle sizes of Cu2O.2Fe3O4 nanocomposites more than that prepared inthe absence of AMPSA/VP (FIG. 8A; Example 2).

The surface morphologies of Cu₂O.2Fe₃O₄ nanocomposites can be determinedby SEM and TEM analyses. SEM of Cu₂O.2Fe₃O₄ nanocomposites arerepresented in FIGS. 9A and 9B. The TEM micrographs of Cu₂O.2Fe₃O₄nanocomposites are illustrated in FIGS. 10A and 10B. High resolution TEMmicrographs are used to confirm the porosity and arrangement ofCu₂O.2Fe₃O₄ nanocomposites as represented in FIG. 11A-D. SEM images ofCu₂O.2Fe₃O₄ nanocomposites prepared in absence of AMPSA/VP (FIG. 9A;Example 2) showed different shapes with different particle sizes as thesmaller ones with 10-30 nm size belong to the Fe₃O₄ nanospheres and thebigger particles with 35-300 nm belong to the rhombic dodecahedral Cu₂O,which is confirmed by TEM of (FIG. 10A). SEM and TEM images ofCu₂O.2Fe₃O₄ nanocomposites prepared in the presence of AMPSA/VP (Example3) represented in FIGS. 9B and 10B confirms the even distribution ofsmall Fe₃O₄ nanospheres and Cu₂O nanocrystals as appeared as black dots.The bright color in FIG. 10B that surrounds the Cu₂O.2Fe₃O₄nanocomposites elucidates the presence of AMPSA/VP as a shell forencapsulation of Cu₂O.2Fe₃O₄ and confirms the proposed structure in FIG.2. The HRTEM image of the Cu₂O.2Fe₃O₄ nanocomposites and the enlargedview of the crystal structures of Cu₂O.2Fe₃O₄ confirms the regulardistribution of Cu₂O.2Fe₃O₄ crystal with porous structure (FIGS. 11B andD) when AMPSA/VP is used to prepare Cu₂O.2Fe₃O₄ nanocomposites.

The DLS measurements of Cu₂O.2Fe₃O₄ nanocomposites were represented inFIGS. 12A and 12B. The hydrodynamic average particle sizes andpolydispersity index (PDI) of Cu₂O.2Fe₃O₄ nanocomposites capped withAMPSA/VP are 15.24 nm and 0.224 nm, respectively (FIG. 12A). The DLSmeasurements of Cu₂O.2Fe₃O₄ nanocomposites prepared in absence ofAMPSA/VP (FIG. 12B) determined the hydrodynamic average particle sizesand PDI as 153.2 nm and 1.285, respectively. The DLS confirmed thatmonodisperse Cu₂O.2Fe₃O₄ nanocomposites were prepared in the presence ofAMPSA/VP poly(ionic liquid).

The zeta potentials of the dispersed Cu₂O.2Fe₃O₄ nanocomposites wasrepresented in FIGS. 13A and 13 B. It was determined that theCu₂O.2Fe₃O₄ nanocomposites capped with AMPSA/VP showed good dispersionstability against aggregation due to their large zeta potential (−35.8mV). The potential of Cu₂O.2Fe₃O₄ nanocomposites prepared in absence ofPIL (Example 2) was less negative and determined as −21.09 mV (FIG.13B). These data confirm the formation of uniform monodisperseCu₂O.2Fe₃O₄ nanocomposites with high charges are less likely toaggregate or form clusters when AMPSA/VP is used as capping and reducingagent.

Epoxy resins cured with polyamine or polyamide hardeners showed goodadhesion with steel due to the formation of networks containing etherand hydroxyl groups. There are some microholes or microcracks producedfrom heat curing exotherms or due to the physical force interactionssuch as van der Waals occurring between the epoxy matrix and which formsa channel affecting the coat performances as anticorrosive coatings. Thedispersability of additives in epoxy matrix is the most importantparameter that is used to overcome the formation of cracks or holes. Inthe present method, Cu₂O.2Fe₃O₄ nanocomposites are used as additives forepoxy matrix. The Cu₂O.2Fe₃O₄ nanocomposites having different weightpercentages ranged from 0.1 to 5 (wt. % based on total weight of epoxyresin and hardener) are dispersed in epoxy resins and cured withpolyamide hardener as illustrated in the experimental section. The blanksample of cured epoxy resins without Cu₂O.2Fe₃O₄ nanocomposites showsholes and microcracks at the epoxy coat surfaces. The dispersion ofCu₂O.2Fe₃O₄ nanocomposites prepared with Example 3 was better than thatprepared by Example 2 due to more negative zeta potential in thepresence of AMPS/VP (FIG. 13). The epoxy network can be bonded with theCu₂O.2Fe₃O₄ nanocomposites surface via either hydrogen bonding with orpolar interactions between charged surfaces of Cu₂O.2Fe₃O₄nanocomposites and hydroxyl or amide groups of cured epoxy matrix tocoat porous spaces for volume expansion of cured epoxy surfaces. It wasexpected that the Cu₂O.2Fe₃O₄ nanocomposites atoms having 3d empty orbitcan be easily bonded with p orbit of active oxygen atoms of hydroxylgroups of cured epoxy curing, providing enough active oxygen atoms withelectrons to form p-d conjugative effect.

The adhesion of epoxy resins with steel substrate using pull-offresistance tester was determined and are provided in Tables 1 and 2. Thedata confirm the increment of adhesion between epoxy composites withincrement of Cu₂O.2Fe₃O₄ nanocomposites contents and steel substrate.The incorporation of Cu₂O.2Fe₃O₄ nanocomposites into epoxy matrix didnot show any significant improvement in adhesion values. These data canbe referred to the increment of attraction forces between the negativecharges on the surfaces of Cu₂O.2Fe₃O₄ nanocomposites and positivecharges of steel which alters by nanogel accumulation. The improvementof mechanical properties of Cu₂O.2Fe₃O₄ nanocomposites such as impactresistance, hardness and abrasion resistance (Tables 1 and 2) confirmsthe good interactions between epoxy and Cu₂O.2Fe₃O₄ nanocomposites. Thisobservation elucidates that formation of Cu₂O.2Fe₃O₄ nanocompositesnetworks improves the ability of epoxy coat to absorb both the abrasionand impact forces.

The anticorrosion performance of epoxy coats on steel substrate can beexamined by salt spray resistance test as summarized in Tables 3 and 4and illustrated in FIGS. 12 and 13. The features the results are testedfrom the appearance of epoxy blistering and steel rust under epoxyfilms. The data confirm no osmotic blisters appeared in epoxy film butthe rust increased more for blank film that was not blended withCu₂O.2Fe₃O₄ nanocomposites. The data (Tables 3, 4) elucidate that theepoxy embedded with Cu₂O.2Fe₃O₄ nanocomposites achieved high salt sprayresistance for 1000 h than other composites while the blank failed after300 h. This can be referred to the higher dispersion efficiency ofCu₂O.2Fe₃O₄ nanocomposites into epoxy matrix forms protective film atthe epoxy surfaces prevents the diffusion of water or salts to reactwith steel surfaces. The negative surface charge increases theinteraction between Cu₂O.2Fe₃O₄ nanocomposites and epoxy matrix andhence their protection properties increased. Careful inspection of dataproves that Cu₂O.2Fe₃O₄ nanocomposites at low content can act asself-healing materials at low concentrations. It was noticed that norust formed at X-cut using low Cu₂O.2Fe₃O₄ nanocomposites. This behaviorcan be due to the high salt resistivity of Cu₂O.2Fe₃O₄ nanocompositeswhich assists in increasing the diffusion of nanoparticles at X cut(defected area).

TABLE 1 Mechanical test of the cured Epoxy Cu₂O•2Fe₃O₄ nanocomposites.Adhesion Abrasion Cu₂O•2Fe₃O₄ (pull off Resistance nanocompositesHardness resistance) Impact weight loss (Example 2) (Newton) MP T-bend(Joule) (mg) 0 3 5 pass 5 65 0.1 7 7 pass 8 19 1.0 10 8 pass 10 14 5.014 10 pass 12 10

TABLE 2 Mechanical test of the cured Epoxy Cu₂O•2Fe₃O₄ nanocompositesAdhesion Abrasion Cu₂O•2Fe₃O₄ (pull off Resistance nanocompositesHardness resistance) Impact weight loss (Example 3) (Newton) MP T-bend(Joule) (mg) 0 3 5 pass 5 65 0.1 5 12 pass 10 12 1.0 8 14 pass 13 9 5.010 17 pass 17 4

TABLE 3 Salt spray resistance of epoxy Cu₂O•2Fe₃O₄ nanocomposites.Cu₂O•2Fe₃O₄ nanocomposites Disbonded area Rating Number (Example 2) cm²% (ASTM D1654) Blank 16.5 9 6 0.1 1.6 1 9 1.0 0.1 0.01 10 5.0 10 5 7

TABLE 4 Salt spray resistance of epoxy Cu₂O•2Fe₃O₄ nanocompositesCu₂O•2Fe₃O₄ nanocomposites Disbonded area Rating Number Method 3 cm² %(ASTM D1654) Blank 16.5 9 6 0.1 1.6 1 9 1.0 0.1 0.01 10 5.0 0.1 0.01 10

Cone calorimeter measurement is used for assessing the fire behavior ofmaterials. It is used to determine the flammability of materials byinvestigating parameters, such as heat release rate and smoke productionrate. The curves of epoxy blank and epoxy blend with 5 wt. % ofCu₂O.2Fe₃O₄ nanocomposites prepared as described in Example 3 are shownin FIGS. 14 and 15. The data confirm that the presence of Cu₂O.2Fe₃O₄nanocomposites form a protective layer which hindered the decompositionof epoxy resin by reducing both heat release rate and smoke productionrate. Moreover, the time of ignition of epoxy increased when it wasblended with 5 wt. % of Cu₂O.2Fe₃O₄ nanocomposites. This illustratedthat 5 wt. % of Cu₂O.2Fe₃O₄ nanocomposites could as fire retardant forepoxy coatings and further enhance the epoxy fire safety. FIG. 15 showsthat the addition of 5 wt. % of Cu₂O.2Fe₃O₄ nanocomposites could furtherdecrease the smoke production rate of epoxy resins. It can be ascribedto the promotion of formation of a compact intumescent char layer onepoxy surface by Cu₂O.2Fe₃O₄ nanocomposites.

It is to be understood that the present invention is not limited to theembodiments described above but encompasses any and all embodimentswithin the scope of the following claims.

We claim:
 1. A method of synthesizing bimetallic oxide nanocompositescomprising the steps of: providing a first metal salt solution adding anoxidizing agent to the first metal salt solution while degassing thefirst metal salt solution with an inert gas; heating the first metalsalt solution to a temperature ranging from about 40° C. to about 65°C.; adding a second metal salt solution to the heated first metal saltsolution to form a reaction mixture; adding a solution comprising a poly(ionic liquid) to the reaction mixture; adding a first base dropwiseinto the reaction mixture for about 1 hour; adding a second base to thereaction mixture while stirring and maintaining temperatures rangingfrom about 40° C. to about 65° C. for at least 2 hours to provide asolution including the bimetallic oxide nanocomposites as precipitate.2. The method of synthesizing bimetallic oxide nanocomposites accordingto claim 1, further comprising the steps of: separating the precipitateby centrifuging at 15000 rpm for about 10 minutes to isolate thebimetallic oxide nanocomposites; and washing the bimetallic oxidenanocomposites with distilled water.
 3. The method of synthesizingbimetallic oxide nanocomposites according to claim 1, wherein theoxidizing agent is sodium sulfite (Na₂SO₃).
 4. The method ofsynthesizing bimetallic oxide nanocomposites according to claim 1,wherein the first metallic salt solution includes FeCl₃, the secondmetallic salt solution includes CuCl₂ and the bimetallic oxidenanocomposites include Cu₂O.2Fe₃O₄.
 5. The method of synthesizingbimetallic oxide nanocomposites according to claim 1, wherein the poly(ionic liquid) is selected from the group consisting of poly(2-acrylamido-2-methyl-1-propanesulfonic acid-diethyl ethanolamine(PAMPS-DEA), 2-acrylamido-2-methyl-1-propanesulfonic acid-N-isopropylacrylamide (AMPS-NIPAm), 2-acrylamido-2-methyl-1-propanesulfonicacid-vinyl pyrrolidone (AMPS-VP), and2-acrylamido-2-methyl-1-propanesulfonic acid-acrylic acid (AMPS-AA). 6.The method of synthesizing bimetallic oxide nanocomposites according toclaim 1, wherein the first base is sodium hydroxide and the second baseis ammonium hydroxide.